(1) Field of the Invention
The present invention relates to the field of supervisory control and data acquisition (SCADA) systems. More particularly, the present invention relates to SCADA systems in which signals from end devices such as sensors and control devices are transmitted to and from a remote location via a standard Modbus or other protocol.
(2) Description of the Related Art
The control of various systems such as may be associated with a vehicle or other complex systems must take in various electronic signals and process those signals to control associated components. These controls are becoming more and more complex. One type of control element is an input/output module. An input/output module receives an “Input” signal, such as from a switch or sensor, respectively a digital or an analog signal. The signal from a sensor might be that a particular condition has been sensed, and some control step should now be taken. The input from a switch may be that the switch has switched from off to on, and some control action must be taken. The “output” of the module is typically sending a signal to control an associated component based upon the signal from the switch or sensor or from a microcontroller. In the past, there has been a plurality of these modules associated with more complex systems. Typically, a single processor (PLC) has been associated with and directly and locally connected to a plurality of input/output modules located in the PLC. This has been somewhat undesirable in that a failure of that single processor would cause all of those control systems to fail.
SCADA systems perform adjustments by modifying set points and other parameters in the processor (PLC) by communicating principally via a network connection, With the network connection generally inside of a Local Area Network (LAN) where communication timing, security and reliability is maintained. The PLC itself is made up of input/output modules (I/O modules) which connect to the sensors producing the information about the state of the process, and the actuators, which provide the action of the control system.
The prior art utilizes fixed-configuration I/O modules local to the host processor (ie. part of the PLC). Due to cost, complexity and non-rugged nature of PLC's, generally, few are used and cover large geographical regions. This requires many long cables to be run from each sensor to the PLC. Sensors are generally clustered together and thus some rugged low cost means is required to substantially reduce the length and number of cables.
Further the National Electrical Code mandates that Wiring and devices used in a hazardous environment be intrinsically safe in that they are incapable of releasing electrical or thermal energy to cause ignition of a volatile gas or gaseous mixture. In general, an intrinsically safe environment has a safe side and a hazardous side. In an intrinsically safe application, it is a common practice to use an intrinsically safe barrier as a safety buffer between a device located on the hazardous side and an apparatus located on the safe side. The prior art therefor requires the addition of Intrinsic Barriers to each input/output signal.